When observing with a microscope, there are times when it is necessary to photograph the observed object. This need is especially great, for example, in the production of semiconductors or in the treatment of affected areas during surgery. In such cases, the use of a stereoscopic microscope that performs three-dimensional observations is common. Furthermore, since it is desirable to be able to connect either a device that records a still picture or a device that records moving pictures to a stereoscopic microscope, the ability to attach either of these two types of recording devices is required. Of these two types, since a high quality image recording device having a wide dynamic range and high resolution is desired for recording still pictures, either a large CCD with a high pixel count or photographic film is commonly used. For recording moving pictures, the required resolution is typically not as high as for recording still pictures; thus, a smaller CCD with less resolution is commonly used.
A stereoscopic microscope is normally formed of an objective lens for substantially collimating a light flux from an object, two afocal zooming optical systems, optical path splitter means for splitting the light fluxes that exit the afocal zooming optical systems into at least one observation system light flux and a photographic system light flux, a binocular tube optical system, and eyepiece lenses for forming magnified images of the observation light flux for viewing. By attaching a stand together with an imaging device to such a stereoscopic microscope, an apparatus that allows viewing as well as photography is achieved.
For a stereoscopic microscope that is to be used for production or medical treatment, it is preferred to have the parts that are near to the observed object be as small as possible. Furthermore, it is preferred that the stereoscopic microscope have the ability to move freely in relation to the stand. In order to accomplish this, the stereoscopic microscope must be made as light as possible so as to enable it to move easily. In addition, the photographic apparatus must be installed to a part of the stand that is separate from the stereoscopic microscope.
In order to arrange the stereoscopic microscope and the photographic apparatus separate from each other, it becomes necessary to lengthen the optical path of the optical system of the photographic apparatus, and it often becomes necessary to provide various attachment positions for multiple image detecting (i.e., photographic) devices by using things such as reflection members. Such an optical system has already been proposed in Japanese Laid-Open Patent Application H11-84263, which provides for an intermediate image plane within a common optical path for the optical systems of the two image detecting devices. However, this design results in the following problems.
When the sizes of the image planes of the two image detecting devices differ greatly, the magnification difference of the optical systems placed between the intermediate image and each of the image planes increases. This places unreasonable demands on the layout of the optical system, thereby resulting in the deterioration of the optical performance which, in turn, necessitates an increase in the number of lens elements needed to maintain satisfactory optical performance.
In order to make the size of an intermediate image that is suited to either a large, high-resolution CCD or a small CCD of less resolution, the magnification of the intermediate image needs to be limited. In conjunction with this, restrictions in the distance settings occur in the imaging device after splitting the light flux so as to provide two optical paths, and the acceptable locations for the placement of the imaging device become greatly diminished. This makes it difficult to arrange the photographing device so that it is located at a position separate from the imaging device so as to enable the observer to make observations while simultaneously working on the object being viewed.